The present invention relates to an apparatus and process for the continuous preparation of a mixture of two or more fluids, such as paints, enamels and dyes, to produce a resulting fluid having desired pre-defined physical properties, such as a particular color, opacity, hue, saturation, luminosity, density and/or viscosity.
Paint production processes have, over the years, evolved from the traditional method of using joint dispersion of pigments to the use of colorimetric processes where there is dispersion of each of the pigments separately to form a set of concentrated pigments (concentrates) and bases which are mixed together at the time of production of the paint to give a determined color. Such colorimetric processes can be classified in two categories, those with adjustment and those without adjustment.
In paint production processes with adjustment, the concentrates are mixed with resins and solvents, or, optionally, with determined bases, and the properties of the resulting mixture are measured. If the measured properties vary from the required specifications, an adjustment is made by the addition of ingredients capable of correcting the variations.
Paint production processes with adjustment are used in factories for the production of medium to large quantities of paints. Mixing occurs in large vats and the end product is only transferred to the final container after confirmation that its properties are within the specified limits.
In paint production processes without adjustment, the base and concentrates are supplied directly to the final container, after which the mixture is homogenised and the paint is ready for use. In such a production process there is no possibility for verification of and adjustments to the end product, and for this reason the base and concentrates have to have rigorously specified properties, and dosage of the base and concentrates has to be carefully controlled so that the end product meets the required specifications.
Paint production processes without adjustment are used, where the paint is to be produced at point of sale, for the supply of relatively small quantities of paint, having a wide range of colors and shades. Such processes can also be used in the factory for the production of small batches of paint.
In processes without adjustment, it is essential that the bases and concentrates are produced within strict limits of variation in color, opacity or hiding power, viscosity and density. The problem with such processes is that it is very difficult to produce the concentrates and bases within such strict limits of variation, only being possible with rigorous control and adjustment, making the process expensive and slow.
The need for such stringent standards of control and the requirement for adjustment mean that the process of producing the bases and concentrates is lengthy and expensive.
The normal methods of controlling and adjusting the bases and concentrates of each batch of paint consist of preparing the concentrate, or base, by culling with standard bases, applying a coat of paint to a substrate, then drying the paint followed by analysis of the color, hiding power and opacity (in the case of the bases) of the dried coat of paint, using visual or preferably spectrophotometric reflection methods. If the paint varies in any of its properties from that which is required, then further ingredients are mixed to compensate for the variation. Once these further ingredients have been added, the resulting concentrate or base is again analysed, and if it is still outside the tolerances for variation of any of the paint properties, another cycle of compensation and analysis is begun. Such a procedure is normally very time consuming, taking days before the paint batch is within its specified tolerance limits.
Also, apart from being time consuming, the traditional methods tend to be very wasteful of paint, because each test batch that does not meet the necessary requirements for color, opacity or hiding power is discarded, without re-using the paint. This can be extremely expensive where a large number of adjustments have to be made before the paint comes within the required specifications.
Efforts to solve such problems have been made, notably, U.S. Pat. No. 4,403,866 describes an apparatus and process for automatically making a paint having the color values of a standard paint, in which components of paint are fed into a mixer where they are combined, and the resulting combination is analysed spectrophotometrically to determine whether it comes within a desired color value. If the paint is not of the desired color, the ratio of paint components fed to the mixer is adjusted until the paint has the required color. Paint mixture that has been analysed and which does not meet the requirements is recycled continuously back into the mixer so that no paint is wasted. However, because the analysed paint is pumped directly back into the mixer the desired component ratio cannot be determined exactly.
There is, therefore, a need for a process in which both concentrates and bases can be analysed and their component ratios can be corrected quickly and simply, and in which paint that does not meet the specified requirements can be re-utilised by the system without adversely affecting the determined component ratios.
In order to cut down paint production costs to a minimum such a process needs to be automatic, with the minimum of human intervention, and to use apparatus which is capable of measuring the properties of the concentrates and bases, determining the ingredients, and quantities thereof required to correct any variations from the required physical properties of the concentrate or base, automatically supplying the correct amount of ingredients necessary to make the correction, and needs to be capable of guaranteeing that the final product has properties that are within the specified limits for the paint.
The object of the present invention is to provide an apparatus and a process for the continuous preparation of fluids, such as paints, enamels and dyes with automatic adjustment of the physical properties of the fluid, and re-utilisation of any fluid that does not have the required physical properties, in order to overcome the above mentioned problems in the state of the art.
According to a first aspect of the present invention, an apparatus for the continuous preparation of a fluid with automatic adjustment of the physical characteristics thereof, comprises:
a storage means, for storing a first component of the fluid;
at least one further storage means, for storing at least one further component of the fluid;
mixing means, for mixing the first component with at least one further component of the fluid, the mixing means having a fluid input and a fluid output;
fluid supply means, connected between the storage means and fluid input of the mixing means, for supplying a specified proportion of each of the components of the fluid to the mixing means;
detector means, for detecting a physical characteristic of the fluid, the detector means being capable of producing a signal representing the detected physical characteristic, the detector means having a fluid input in communication with the fluid output of the mixing means and having a fluid output;
control means, adapted to receive the signal representing the detected physical characteristic, the control means being capable of comparing the detected physical characteristic with a desired physical characteristic of the fluid, and of producing a fluid supply control signal, dependent on the comparison between detected and desired physical characteristics, the fluid supply means being responsive to the fluid supply control signal to vary the proportion of each component of the fluid supplied to the mixing means, until the detected physical characteristic is substantially the same as the desired physical characteristic; and
fluid recycling means, connected between the fluid output of the detector means and the input of the mixing means to allow fluid to return to the mixing means;
wherein the recycling means comprises buffer means, for temporary storage of the fluid, the control means being adapted to produce a buffer control signal and the buffer means being responsive thereto, for controlled supply of the diluted fluid to the mixing means.
For preference, the apparatus additionally comprises fluid dilution means, connected between the output of the mixing means and input of the detector means, for controlled dilution of the fluid before detection of the physical characteristic thereof.
Preferably, the fluid dilution means comprises further mixing means.
More preferably still, the detector means is adapted to measure the transmission of electromagnetic radiation through the fluid, and the signal representing the physical characteristic is obtained by measurement of the transmission of electromagnetic radiation through the fluid.
According to a second aspect of the present invention, a process for the continuous preparation of a fluid with automatic adjustment of the physical characteristics thereof, comprising the steps of:
(i)xe2x80x94supplying a first component of the fluid to a mixing means;
(ii)xe2x80x94supplying at least one further component of the fluid to the mixing means, each of the components of the fluid being supplied in specified a proportion;
(iii)xe2x80x94mixing the components of the fluid;
(iv)xe2x80x94supplying the mixed fluid to a detector means;
(v)xe2x80x94detecting a physical characteristic of the fluid;
(vi)xe2x80x94comparing the detected physical characteristic of the fluid with a desired physical characteristic thereof;
(vii)xe2x80x94varying the specified proportion of the components of the fluid being supplied to the mixing means, until the detected physical characteristic is substantially the same as the desired physical characteristic; and
xe2x80x94(viii) recycling the mixed fluid supplied to the detector means;
such that the step of recycling the mixed fluid supplied to the detector means includes the steps of supplying the fluid to a buffer means and controlling the supply of the fluid from the buffer means to the mixing means, for mixing with the components of the fluid.
For preference, the process further includes the step of diluting the mixed fluid before it is supplied to the detector means.
Preferably, the step of diluting the mixed fluid includes supplying it to a further mixing means.
More preferably still, the step of detecting a physical characteristic of the fluid includes measuring the transmission of electromagnetic radiation therethrough.